Field of the Invention
The present invention relates to an auto-focus (AF) control technology in an imaging system having a lens unit that can be installed in a camera body.
Description of the Related Art
In order to drive a focus lens in an imaging apparatus, a driving amount of the lens is determined based on focus sensitivity. The focus sensitivity is a coefficient for converting a defocus amount detected by the imaging apparatus into a driving amount of the focus lens. In an interchangeable lens type camera system, the focus sensitivity is determined based on optical information of the interchangeable lens.
In Japanese Patent Laid-Open No. S59-151116, a camera system in which the focus sensitivity is variable depending on focal length information of the lens is disclosed. Using the camera system discussed in Japanese Patent Laid-Open No. S59-151116, it is possible to appropriately set the focus sensitivity depending on the focal length and reduce a focusing time. In addition, in Japanese Patent Laid-Open No. 2014-29353, a method of determining defocus correction data based on a camera state such as a spatial frequency is disclosed.
Here, practical focus sensitivity is changed depending on a focus detection position (image height) as well as focal length information of the lens. The technique of the related art disclosed in Japanese Patent Laid-Open No. S59-151116 fails to consider a change of the focus sensitivity depending on the image height. For this reason, it is difficult to set the focus sensitivity suitable for focusing of the surrounding image height and perform accurate focus control in the event of hunting or the like. In order to acquire more accurate focus sensitivity, it is necessary to acquire focus sensitivity for every image height.
On the other hand, the focus sensitivity information is received in communication through a mount terminal between the camera body and the interchangeable lens. The technique of the related art disclosed in Japanese Patent Laid-Open No. 2014-29353 fails to consider a change of the data in communication depending on the image height. If different data is transmitted for each image height, a communication data amount increases as the focus correction accuracy at the surrounding image height increases. In this case, it is necessary to transmit or receive necessary data within a limited communication band between the camera body and the interchangeable lens.